Technical Field
The present invention pertains to a knee-ankle prosthesis for lower-limb amputees and in particular to a hydraulic system for the articulation of the knee and ankle controlled by a microprocessor.
Description of the Related Art
It is common knowledge that prostheses for femoral amputees generally consist of a prosthetic knee and a foot-ankle assembly. There are multiple types of prosthetic knees; however, there are two broad distinct categories: passive knees and active knees.
Passive mechatronic knees are controlled by microprocessors, and are referred to as passive since they do not provide energy but rather use the energy derived from walking. They contain a hydraulic or magnetorheological damper that controls the flexion and extension movements of the knee, through the use of one or several solenoid valves, of which the flow is managed by a microprocessor. The braking action of the damper is strong in the stance phase in order to avoid falling and weak during the swing phase to guide the pendular motion of the leg.
As for active knees, they include a motor that provides energy in addition to the energy derived from walking.
All these knees contain several sensors that allow determining the timing of changing the positions of the solenoid valves or changing the motor torque. The sensors allow the recognition of the exact point in the walking movements at which the leg is currently in, such as the stance phase or swing phase for example, and they also allow measuring the walking speed.
The latest prosthetics are based on the recognition of the situation in which the amputee is (slope, stairs, seated, etc.) such as the Genium® (passive knee marketed by Otto Bock) and the POWER KNEE® (active knee marketed by Össur-Victhom) which has been described in particular in the U.S. patent applications US 2004/0111163 and US 2006/0122711. Situation recognition requires using a large number of sensors and more elaborate recognition algorithms. Recognizing these situations allows adapting the flexion and extension resistance setting as per the situation encountered by the person wearing the prosthetic.
The C-Leg®, marketed by Otto Bock, is particularly well-known, and is historically the first passive knee with hydraulic dampers controlled by microprocessors in the stance and swing phase. This knee has been described in particular in the international patent application WO 96/41599 and in the European patent application EP549855. It controls the flexion and extension for the entire walking cycle (in stance phase and swing phase). Recently, Otto Bock has launched the Genium® knee, which is a significant step forward over the C-Leg. This knee is still a passive knee, but contains numerous improvements related to the recognition of complex situations such as climbing stairs, slopes, seated position, etc.
Another well-known knee is the RHEO KNEE®, marketed by Össur, which is a magnetorheological damper based passive knee. This knee has been described in particular in the U.S. patent application US 2005/0283257 and international patent application WO 2005/087144.
Analytical studies of the movements have shown that while descending stairs, the braking torque of the C-Leg® prosthetic knee remains lower than the braking torque of the contralateral limb. This results in a “fall” on the contralateral limb and a significant increase in the effort taken by it. This effort results in an increase in the joint torques in the entire contralateral limb. Moreover, in order to descend stairs with a “conventional” knee, the prosthetic foot must be placed on the ground on the nose of the step in order to allow the foot to roll and the tibia to advance. This placement must be precise, which requires extra attention from the user. Persons wearing prosthetics thus avoid descending stairs in alternating steps if the stairs are too rough or if the floor is too slippery, etc.
There are also foot-ankle prosthesis which can be classified into the following three categories: purely passive ankles, passive mechatronic ankles with solenoid valves and active mechatronic ankles Purely passive ankles include neither sensors nor solenoid valves nor any machines. Passive ankles with solenoid valves allow controlling the hydraulic dampening action and the mechatronic ankles have sensors, solenoid valves or a motor.
The PROPRIO FOOT® foot-ankle, marketed by Össur and disclosed particularly in the U.S. patent applications US 2005/0197717 and US 20070050047, is a mechatronic prosthesis of which the ankle consists of an electrical motor controller by sensors. Such an arrangement allows relieving the end of the foot during the swing phase to avoid it from damaging the floor; it also allows modifying the heel height setting (if the user is changing shoes), adapting the angle of the ankle in the stance phase depending on the slope and while using stairs, this adaptation always takes place when the user's weight is off the ankle, in the pendular phase, and modifying the ankle angle when in seated position and when transitioning from seated to standing position and vice-versa.
It will be noted that, even though the motor works only during the swing phase, it is already very large, noisy and consumes a lot of energy since it is the motor that allows moving the leg in the swing phase in each step. The ProprioFoot® forces the user to carry a large battery around and to recharge it every day. Moreover, the motor is likely to be noisy.
There is another foot-ankle, the Echelon®, marketed by Endolite and described in particular in the international patent claim WO2008103917, which is a purely passive ankle that consists of a small linear hydraulic damper which allows a mobility of 3° in dorsiflexion (direction of rotation of the foot in which the big toe is raised upwards) and 6° in plantiflexion (direction of rotation of the foot in which the big toe is pushed downwards). Two valves with manually adjustable tips allow adjusting the flow of dorsiflexion and plantiflexion separately. The plantiflexion is particularly important for descending stairs, which allows quickly placing the flat of the foot on the ground.
However, mobility in dorsiflexion is limited)(3°). This compromise allows satisfactory walking on flat surfaces and while climbing up a slope.
Moreover, the Elan® is a passive mechatronic ankle, which is a developed version of the Echelon® foot-ankle that consisted of manual dorsiflexion and plantiflexion valves that have been replaced by solenoid valves. This allows adjusting the hydraulic dampening depending on the slope and walking speed, and the amounts of mobility in dorsiflexion and plantiflexion have not been modified. This solution allows modifying the hydraulic resistances only when a change in slope is detected, i.e., less frequently, which lowers the battery consumption. It is possible to increase the amount of the dorsiflexion while climbing and the amount of plantiflexion when descending. However, such a solution appears to be limited owing to reasons of space requirement.
There is also the Motion Foot foot-ankle, marketed by Fillauer, which is a purely passive ankle with a functioning similar to that of the Echelon®, the only difference being that the hydraulic cylinder is rotary and not linear, as well as the Raize® foot-ankle, marketed by Fillauer and described in the U.S. Pat. No. 6,443,993 in particular, which is a mechatronic passive ankle that consists of a linear hydraulic damper controlled by a valve, which in turn is controlled by microprocessors and sensors. The valve is adjusted continuously and allows controlling the resistance and amplitude of the dorsiflexion as well as the resistance of the plantiflexion. The functions executed are thus more important than the Elan®, marketed by Endolite, but the valve is continuously controlled, which consumes a high amount of energy.
In the same manner as the Echelon® marketed by Endolite, the Raize™ does not move in the swing phase.
None of these ankles (Echelon®, Elan®, Raize™) thus allow increasing the distance from the big toe to the floor during the swing phase. The person wearing the prosthesis will increase this distance by lifting his pelvis from the side of the prosthesis during the swing phase. This strategy expends a lot of energy (elevation of the center of mass) and results in twisting of the pelvis and the lower back.
Lastly, there are many knee-ankles such as the Hydracadence, which is described in particular in the U.S. Pat. No. 2,478,721, which is a knee-ankle assembly that contains a hydraulic damper that controls the angle of the knee, and another hydraulic damper that manages the angle of the ankle There is a hydraulic connection between these 2 cylinders which allows coordination between the angle of the ankle and the angle of the knee. The function carried out by this knee is flexion of the ankle during the pendular phase, which allows avoiding damaging the bottom of the foot against the floor and this dorsiflexion in the swing phase being a result of the flexion of the knee, adjusting the dorsiflexion stopper allows adjusting the prosthesis as per the change in footwear (heel height), and free plantiflexion that facilitates the heel strike.
This knee-ankle consists of one valve that controls the adjustment of the dampening of the knee in the pendular phase. Moreover, this prosthesis, which was designed in the 1940s, does not include any mechatronics and thus cannot adapt to different walking situations.